The present invention relates to ultrasound imaging systems that produce images of eye structures.
Ultrasound has provided physicians, ophthalmologists, and others the ability to examine eye structures without invasive surgery. An ultrasound transducer sends an ultrasound signal into an eye (and possibly surrounding tissue as well) and "listens" for signal echoes. A signal echo indicates the location of a change in impedance (a function of material density and stiffness) within the eye structures. The intensity of the echo signal indicates the amount of the change in impedance. The ultrasound signals detect not only typical eye structures such as the cornea, retina, sclera, etc., but also aberrations such as tumors and blood trapped within an eye's vitreous.
A known version of the Mentor Ophthalmics Advent A/B.TM. System processes ultrasound signals to create images of eye structures by displaying the different ultrasound signal intensities in one of 256 shades of grey. Since the human eye has some difficulty in differentiating close shades of grey, the Advent A/B.TM. System provides operators with tools to alter the image to prevent display limitations from impairing a physician's ability to differentiate eye structures.
One such tool is a set of user-selectable "gamma curves." A gamma curve basically describes a display characteristic such as brightness as a function of echo signal intensity (the term brightness as used herein encompasses the location of a shade of grey on a grey scale). One such gamma curve in the Advent A/B.TM. System simply equates brightness with signal intensity in a linear fashion. The Advent A/B.TM. System also provides non-linear curves such as an "S Curve." The "S Curve" gamma curve has a relatively small slope at low and high signal intensities and has a relatively large slope at intermediate signal intensities. All the gamma curves are monotonic (i.e. the slope of each gamma curve is either always positive or always negative). Though the system contains color output ports, the image is monochromatic. The user can select a single color (e.g. white, sepia, etc.), which is displayed with varying degrees of brightness at different points in the image depending on the different echo signal intensities.
The known version of the Advent A/B.TM. System also provides a "gain knob" to help the user alter the image. By turning the knob, the user adjusts a constant or proportionality associated with any one of the gamma curves, so that the brightness that the gamma curve associates with every echo signal intensity is either increased or decreased.
The user selectable gamma curves and the gain knob allow the user to increase the visual contrast between different features of interest in the image and aid the user in the search for structure boundaries.
The Advent A/B.TM. System also supports "temporal averaging." Temporal averaging consists of storing ultrasound signal data for each image point over multiple scans and creating an image where each image point's shade of grey depends on the average value of the image point over the multiple scans.
An article by Gonzalo R. Diaz entitled "Ultrasound Color Imaging" suggests strategically adding color hues to ultrasound images that also include shades of grey. In particular, the article suggests that a user be allowed to substitute one or more color hues for one or more grey shades. The article states that the colored regions in the display provide good contrast against the remaining, predominately grey image. An accompanying color photograph entitled "Eye Ultrasound" includes various grey shades along with certain regions colored with various color hues. It appears that some closely similar hues were substituted for some closely similar grey shades. There does not appear to be a continuous gradation from the grey shades to the color hues; rather the image appears to abruptly juxtapose grey shades with color hues.
Certain corneal topography systems create color coded topographical maps that use different colors to show different amounts of deviation from an ideal surface. Doppler ultrasound imaging systems have used color to represent blood velocity. Certain magnetic resonance imaging (M.R.I.) systems and computer aided tomography (C.A.T.) scanners use multi-colored images to help physicians differentiate structures of interest.